Radical Islamic parties vowed on Friday to defy a Pakistani government ban on the use of mosque loudspeakers to make calls of support for the Taliban in Afghanistan.

The government, increasingly sensitive to criticism of its support for the US military campaign in Afghanistan, issued a decree this week saying mosque loudspeakers could only be used for calls to prayer and Friday sermons.

Security was increased in all major cities, including Quetta, Lahore and Peshawar, in case of demonstrations after mosques emptied on Friday. Officials said mosque sermons would be recorded by police.

Anti-US fervour was heightened by a reported call from accused terrorist leader Osama bin Laden for Pakistani Muslims to "confront the crusade against Islam".

A statement which Arab satellite television channel Al-Jazeera said came from bin Laden accused the Pakistani government of "standing under the banner of the Cross while Muslims are being slaughtered in Afghanistan".

And leaders of religious parties said there would be demonstrations and speeches in mosques criticising the government for supporting the United States.

"We are in a movement and our prayer leaders will continue to inform Muslims what this government is doing against Islam," said Mufti Mohammad Jamil, central information secretary of the radical Jamiat Ulema-e-Islam (JUI).

The fundamentalist Jamaat-i-Islami (JI) also condemned the government action to quieten mosque loudspeakers.

"We condemn this decision as they cannot stop a prayer leader making speeches against attacks on Muslims in Afghanistan," JI deputy chief Ghafoor Ahmed said.

The Pakistani government, which has stepped up pressure on Islamic parties since the US began bombing Afghanistan on October 7, on Wednesday ordered a ban on the use of mosque loudspeakers for non-religious use.

"We will monitor speeches and legal action will be taken against anyone who tries to instigate or incite people," the Sindh province home secretary, Brigadier Mukhtar Sheikh, told AFP. Sindh includes Karachi, the country's biggest and most restive city.

Police have been asked to record Friday prayer speeches, he said adding: "We will not allow anyone to politicize prayer speeches in mosques."

The JI and JUI have called for followers to demonstrate after Friday prayers against the United States and the Pakistani government support.

Police have tightened security in Karachi and paramilitary troops have been deployed outside big mosques and religious schools.

"We have no objection to peaceful demonstrations but no rallies and processions are allowed," Sheikh said.

President Pervez Musharraf told a security meeting on Wednesday that no-one would be allowed to challenge the authority of the government and those making seditious speeches would be prosecuted.

His words were seen as a warning to fundamentalist party leaders who have called him a "traitor" for siding with the United States instead of the hardline Islamic Taliban militia in neighboring Afghanistan.

Some 50,000 Islamic militants held a protest march in Karachi last week -- the biggest anti-US rally in Pakistan since the US military campaign in Afghanistan started -- KARACHI (AFP)